Implement MD5 in the digest module

[jedestep]

While binding to a wide variety of existing C reference implementations of MD5 is ok, I feel like MD5 is widely used enough that extra::digest really deserves a native implementation.

[JeffMurray]

From a totally new to Rust perspective:

I thought brson had a cripto-rust repo that includes an MD5, but I cant seem to find it at the moment. Not that I have figured out how to use those things yet,

I would like a native way to get an MD5 as well. I would even appreciate an example how to use a repo that looks like an interface. When I look at things like brsons cripto-rust repo or pcwalten's spidermonkeny interface, I do not know the steps to compile them.

[huonw]

@JeffMurray you may've been thinking of rustcrypto, which appears to just be wrapper around libcrypto for the hashes.

[zslayton]

@huonw I'd like to work on this. Would I be stepping on anyone's toes?

[huonw]

@zslayton not that I know of, although @DaGenix (enix on IRC) has been working on the SHA ones.

[DaGenix]

I'm actually planning on submitting a pull request tommorrow that includes an md5 implementation. I would certainly appreciate extra eyes for review / improvement. That request will also include much better support for future hash algorithms.

[kud1ing]

See PR #8097

[kud1ing]

See also https://github.com/alco/rust-digest

CC @alco

[DaGenix]

See PR #8272

[alexcrichton]

Closing, we have decided to not distribute crypto code as part of the standard library.